August 13, 2013

Safe Sugar Dose In Humans Proves Toxic To Mice

Using a novel study approach, researchers at the University of Utah found a high-sugar diet considered borderline-safe for human consumption can increase mortality and reduce vigor in mice.

Researchers said the sugary diet had a similar effect to being the inbred offspring of first cousins in the mice they observed.

"Our results provide evidence that added sugar consumed at concentrations currently considered safe exerts dramatic adverse impacts on mammalian health," the researchers noted in their study published today in Nature Communications.

"This demonstrates the adverse effects of added sugars at human-relevant levels," said study co-author Wayne Potts, a University of Utah biology professor.

The mice were given a diet that included 25 percent "added sugar" – the equivalent of three cans of sugary soda per day in humans. While the mice on the high-sugar diet didn’t exhibit significant metabolic symptoms, they “died more often and tended to have fewer babies," said co-author James Ruff, a recent PhD graduate from the University of Utah.

For the study, the Utah researchers erected room-sized “mouse barns” in an attempt to replicate natural territorial and mating behaviors in the rodents. The team also used mice descended from wild house mice to eliminate the domesticating influences of breeding laboratory mice.

"They are highly competitive over food, nesting sites and territories," Potts said. "This competition demands high performance from their bodies, so if there is a defect in any physiological systems, they tend to do more poorly during high competition."

Potts dubbed the novel testing approach the Organismal Performance Assay, or OPA, which he said places the experiment in a more natural context and enables the examination of nuanced changes in behavior.

"When you look at a mouse in a cage, it's like trying to evaluate the performance of a car by turning it on in a garage," Ruff says. "If it doesn't turn on, you've got a problem. But just because it does turn on, doesn't mean you don't have a problem. To really test it, you take it out on the road."

The researchers started with over 150 “founder" mice that weaned at four weeks and then assigned either the sugary diet or the control diet, with males and females evenly split on each diet. After being kept in same-sex cages to prevent breeding for 26 weeks, all the mice were then placed in the mouse barns to compete with each other and breed for 32 weeks while being given the sugary diet.

After the 32-week period, the researchers found 35 percent of the extra-sugar females died – double the 17 percent death rate for the female control group. While the males didn’t exhibit a difference in mortality rates, the extra-sugar males dominated 26 percent fewer territories than males on the control diet. Males on the high sugar diet also produced 25 percent fewer offspring than their peers in the control group.

Potts said the National Research Council’s recommendation for humans suggests that no more than 25 percent of calories should be from "added sugar," the dose given by his research team.

“The dose we selected is consumed by 13 percent to 25 percent of Americans,” he noted.